1. Field of Invention
The present invention relate to a pretensioner for a seat belt. More particularly, it relates to a pretensioner for a seat belt that reduces injury of the passenger's chest by preventing load applied to the passenger's chest from increasing, by allowing a compressed gas, which is generated in a cylinder when a rack used for the pretensioner moves down, to be discharged to the outside while rotating along a spiral guide blade formed in a micro gas generator.
2. Description of Related Art
Vehicles are generally equipped with three-point type of seat belts composed of a waist belt 10 surrounding the waist of a passenger and a shoulder belt 20 surrounding a shoulder and the chest of the passenger, a shown in FIG. 1, in order to safely protect a driver and passengers in an accident.
The seat belt is designed to be locked in a collision of a vehicle, but the belt is loosened rather than fastened for a short time until before the belt is wound from the collision, such that the passenger may be released from the seat and hit against the windshield or the side of the door.
A pretensioner that is one of means for actively winding the loosened belt winds back a belt by using the explosion force of an MGG (Micro Gas Generator), by sensing a shock generated in a vehicle.
A typical pretensioner using explosion pressure uses a rack and a pinion, in which the rack 60 inserted in a cylinder 50 is engaged with a pinion 70. In an accident, a micro gas generator 51 explodes and discharges an expansion gas into the cylinder 50, such that the rack 60 is pushed back and the pinion 70 is rotated by the pressure.
The rotational force of the pinion 70 is transmitted to a cylindrical spool wound with the webbing of a seat belt through a clutch unit, such that the spool is reversed within a short time, thereby winding the belt.
The operation of a pretensioner of the related art is described with reference to FIGS. 2A-2E. When a current is applied to an MGG in a car collision, powder explodes and pushes up the rack 60 (a). As the rack 60 moves up, the pinion 70 engaged with the rack rotates and winds a cylindrical spool 90 wound with the belt, such that a passenger is rapidly restricted (b).
When energy is transmitted to the passenger and the upper body moves forward, the pinion 70 is reverses and the rack 60 moves down to reduce the load transmitted to the passenger's chest by the spool 90. The gas in the cylinder 50 is compressed by the rack 60 moving down and the compressed gas interferes with the moving-down of the rack, such that the passenger's chest is pressed (c).
Thereafter, as the rack 60 keeps move down, the gas is maximally compressed and the load applied to the passenger's chest increases, such that the passenger's chest is more injured.
The information disclosed in this Background section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.